Evaluation of siRNA uptake and functional activity in a human organotypic skin mo

Kaspar, Roger

Abstract

Although RNA interference offers high potential as a novel therapeutic approach for treating skin disorders, delivery concerns have hampered their progression to the clinic. The most efficient and effective way to deliver functionally-active siRNA is through intradermal injection. We have shown that the high pressure generated by intradermal injection of large volumes is sufficient to deliver nucleic acid to skin (similar to what is observed in high pressure tail vein injection that delivers siRNA to the liver). Indeed, the intradermal injection of large volumes of our lead clinical siRNA inhibitor TD101 to foot lesions led to marked improvement in pachyonychia congenita symptoms in a recently completed Phase 1b clinical trial. The intense pain associated with this mode of administration (oral pain medication and regional nerve blocks were required to mitigate the pain) appears to prevent future use of this method. The use of intradermal injection bypasses the stratum corneum barrier and also provides a hydrodynamic pressure that appears to facilitate siRNA uptake by keratinocytes. We, and others, have developed patient-friendly technologies that allow siRNA to be delivered across the stratum corneum barrier, including a topical formulation (GeneCream) as well as hollow dissolvable microneedle arrays that penetrate into the epidermis and release their siRNA cargo. Unfortunately, without the pressure associated with injection of high volumes, little functional siRNA enters the cell. Our long-term goal is to identify patient-friendly technologies that will allow effective and efficient siRNA delivery into the appropriate skin compartment and also facilitate uptake by keratinocytes and incorporation into the RNA induced silencing complex (RISC). In this Phase I proposal, we develop a human epidermal equivalent system (i.e. regenerated human skin), in which pre-existing gene expression (CD44, mutant keratin 6a and/or reporter) can be monitored. This model system will be used to evaluate and optimize Traversa's PTD-DRBD siRNA delivery technology (facilitates siRNA uptake by cells) as well as other commercially-available delivery uptake technologies including Invivofectamine, Accell, etc. The most promising of these will be used in combination with our stratum corneum delivery technologies (GeneCream, microneedle arrays and/or iontophoresis). Skin equivalents will be prepared from transduced (with EGFP reporter) or untreated normal primary human keratinocytes as well as keratinocytes derived from pachyonychia congenita patient biopsies. In Phase 2, the best technologies identified in Phase 1 will be tested in mouse models including immunocompromised mice harboring human skin grafts. The most effective combination(s) of these technologies will then be subjected to toxicology and pharmacokinetics studies in preparation for evaluation in the clinic.

Public Health Relevance

Despite the exciting discoveries of the underlying genes and mutations responsible for a large number of skin disorders, few if any novel clinical treatments have emerged. The purpose of this proposal is to exploit RNA interference to selectively inhibit expression of disease-relevant genes. In Phase 1, we develop human skin equivalents (organotypic skin model) in which gene expression can be readily monitored for successful delivery of functional siRNA and test siRNA technologies that facilitate siRNA uptake by skin keratinocytes in combination with existing technologies that allow delivery across the stratum corneum skin barrier. In Phase 2, we will test the technology developed in Phase 1 in animal models. The best combination(s) of technologies will be further evaluated under GLP conditions in animal toxicology and pharmacokinetic assays in preparation for human trials.